backlight might be controlled with video.ko driver by setting kernel command line acpi_osi="Windows 2001" to claim it as Windows XP on Y,W,T,R 6 and 7.

A BIOS writer in Panasonic said me that they have an internal rule not to enable features which is not tested on the OS.
They only tested on Windows XP and vista, then they did not enable ACPI video interface for linux.

ubuntu may have a driver and interface to control through acpi video driver. see /proc/acpi/video/